This causes abiword to treat the contained svg data just like
it does png data, in that, it does nothing with it and just
passes it on to the Image classes which can make use of it
for display.

So now the svg data is loaded, saved, read, etc properly.
All that's left is work in af/gr/xp/gr_VectorImage.cpp to
read in the svg data and display it. We'll need to expand
the functionality of af/gr/xp/gr_Graphics, as well, however,
to get a good subset of svg going.